Process for preparing environmentally stable products by the remediation of contaminated sediments and soils

ABSTRACT

This invention relates to thermo-chemical remediation and decontamination of sediments and soils contaminated with organic contaminants as well as inorganic materials with subsequent beneficial reuse. Novel environmentally stable products of commercial value are produced when certain additives such as calcium and metal oxides are mixed with the contaminated materials. In the process, the mixture is heated to 1150° C.˜1500° C. to produce a molten reaction product with at least part of an excess amount of oxygen mixture or air is continuously bubbled through the melt in order to provide mixing and achieve high thermal destruction and removal efficiencies of the organic contaminants. The melt is then quickly quenched in moist air, steam, or water to avoid the transformation of the amorphous material into crystals. The inorganic contaminants such as chromium, nickel, zinc, etc. are incorporated and completely immobilized within the amorphous silicate network. Atmospheric emissions resulting from this process are nontoxic and capable of meeting currently specified health and environmental requirements. 
     The amorphous material can be pulverized to yield a powder which evinces cementitious properties either by reaction with alkali solution or by blending it with other materials to produce blended cements. The compressive strengths of the concretes made from the powder of the subject invention and blends thereof are comparable to, or greater than the ASTM requirements for general purpose concrete applications. The powder of the subject invention, blended cements, and concrete/mortar derived therefrom also easily pass the EPA TCLP leach test to achieve environmental acceptability.

FIELD OF THE INVENTION

This invention relates to thermo-chemical remediation anddecontamination of sediments and soils contaminated with various organicand inorganic compounds. Novel environmentally stable products aregenerated in conjunction with the remediation process when additivessuch as calcium and metal oxides are added to the contaminatedmaterials.

BACKGROUND OF THE INVENTION

All types of man-made contaminated materials that pollute ourenvironment are generated worldwide. These contaminants are found inair, water, river sediments, manufactured town gas sites, etc. There aretwo general types of contaminants: organic and inorganic. The mostprevalent organic contaminants associated with sediments and soilsinclude: Polynuclear aromatic hydrocarbons (PAHs), chlorinatedhydrocarbons such as polychlorinated biphenyls (PCBs), dioxins, furans,etc. and fossil-fuel derived hydrocarbons and their derivatives. Themost common inorganic contaminants include volatile and nonvolatileheavy metals and mineral-derived materials such as asbestos.

Current thermal methods for the treatment of the above waste materialsinclude the following four treatment systems: vitrification, plasmaprocessing, molten metal processing and steam reforming. None of thesemethods have proven sufficiently economical for large-scaledecontamination applications. In addition, after treatment, thesetechnologies generate large secondary, waste streams that requireexpensive disposal.

This invention teaches a novel thermo-chemical transformation ofcontaminated sediments and soils into useful products for generalconstruction applications, namely, blended cements and thus cansignificantly improve remediation economics by creating such value-addedend products.

SUMMARY OF THE INVENTION

The principal benefit of the present invention is to provide aneconomical method for remediating sediments and soils contaminated withorganic as well as inorganic contaminants by:

a) ensuring high thermal destruction (99.99% or more) of organiccontaminants present in the sediments and soils by converting thecontaminants into nonhazardous compounds, such as CO₂, H₂ O and CaCl₂ ;

b) providing a process for incorporating and immobilizing inorganiccontaminants such as heavy metals in an amorphous leach-resistantsilicate network;

c) transforming the contaminated sediments and soils into usefulconstruction products.

Another advantage of the invention is the ability to impart specificdesirable reactivity properties to decontaminated sediments and soils byreaction with appropriate amounts of limestone, alumina, ferric oxidesand fluxing agent during the melting stage in the presence of excessoxygen or oxygen-containing gas.

An additional advantage of the invention is a new waste managementtreatment technology to replace landfill and incineration methods.

These, and other benefits and advantages, are embodied in the subjectinvention which relates to a novel process for the remediation ofhazardous materials comprised of sediments and soils which arecontaminated by organic contaminants such as PAHs, PCBs, dioxins,furans, etc. and inorganic contaminants such as volatile and nonvolatileheavy metals. The organic contaminants are volatilized from thecontaminated sediments and soils due to the elevated temperatures, 1150°C. to 1500° C., encountered in the subject process. The volatilizedorganic contaminants are thermally destroyed with destruction andremoval efficiencies exceeding 99.99 percent by reaction with the excessoxygen present in the reaction chamber. The organic contaminant-depletedsediments and soils then further react with proper amounts of limestone,alumina, ferric oxides and other suitable additives which are added tothe contaminated mixture to produce an amorphous molten reaction productwithin which the inorganic contaminants and heavy metal cations such aslead, cadmium, arsenic, barium, chromium, mercury, selenium, silver,etc. in the form of their stable oxides are incorporated and immobilizedin the silicate network. The molten reaction product is quickly quenchedin moist air, steam or water to ambient temperature to avoid thetransformation of the amorphous material into crystals and thus enhancethe possibilities for the heavy metal cations to become incorporated inthe amorphous non-crystalline material. The quenched melt is thenpulverized to yield the reactive melt of the subject invention.

Thus, the process of the subject invention includes the thermo-chemicalremediation and decontamination of sediments and soils contaminated withorganic contaminants as well as inorganic contaminants and comprises thesteps of: combining the contaminated sediments or soils with a mixtureof calcium oxide source, alumina, ferric oxides and fluxing agent;heating the mixture to produce a molten reaction product; bubblingoxygen through the melt for destruction of the organic contaminants;quenching the melt in the presence of moist air, steam, or water to forman amorphous material; pulverizing the amorphous material to form apowder; and blending the powder with a cement to yield a blended cement.The product of the subject invention comprises the reactive melt productof claim 2, further including magnesia (MgO), alkalis (Na₂ O and K₂ O),sulfur trioxide (SO₃) present as gypsum, phosphorus oxide (P₂ O₅),titanium oxide (TiO₂) and strontium oxide (SrO).

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an x-ray diffraction graph of the subject invention.

FIG. 2 is an x-ray diffraction graph of the sediment from which thereactive melt of FIG. 1 was prepared.

FIG. 3 is an x-ray diffraction graph of commercial portland cement.

FIG. 4 is an x-ray diffraction graph of a blended cement produced from40 wt % reactive melt and 60 wt % type I portland cement.

FIG. 5 is an x-ray diffraction graph of a blended cement produced from70 wt % reactive melt and 30 wt % type I portland cement.

FIG. 6 is an x-ray diffraction graph of a commercial portland cementmortar.

FIG. 7 is an x-ray diffraction graph of blended cement mortar.

FIG. 8 is a schematic showing the manufacture of reactive melt by thesubject invention using a cupola.

FIG. 9 is a schematic showing the manufacture of reactive melt by thesubject invention using a natural-gas-fired melting furnace.

FIG. 10 is a schematic showing the manufacture of reactive melt by thesubject invention using an electric melting furnace.

DETAILED DESCRIPTION OF THE DRAWINGS

A process of the present invention involves introducing raw feedmaterials such as contaminated sediments and soils, lime, metal oxidesand fluxing agents that contain chemical compounds necessary for theproduction of reactive melt into a furnace in proper proportions, morespecifically, the process of the subject invention includes thethermo-chemical remediation and decontamination of sediments and soilscontaminated with organic contaminants as well as inorganic contaminantsand comprises the steps of: combining the contaminated sediments orsoils with a mixture of calcium oxide source, alumina, ferric oxides andfluxing agent; heating the mixture to produce a molten reaction product;bubbling oxygen through the melt for destruction of the organiccontaminants; quenching the melt in the presence of moist air, steam, orwater to form an amorphous material; pulverizing the amorphous materialto form a powder; and blending the powder with a cement to yield ablended cement.

Exemplary reactive melt may be found when a sediment (Table 1)remediated by the process contains about 20 to about 40 weight percentlime (CaO), about 45 to about 65 weight percent silica (SiO), about 5 toabout 20 weight percent alumina (Al₂ O₃), about 2 to about 10 weightpercent ferric oxide (Fe₂ O₃), about 0.1 to about 5 weight percentsulfur trioxide (SO₃) present as gypsum, about 1 to about 3 weightpercent magnesia (MgO), about 0.1 to about 5 weight percent alkalis (Na₂O and K₂ O), and about 0 to 5 weight percent fluxing agent. Theproperties of the resulting reactive melt may be modified throughcombination with a portland cement.

The amorphous nature of the reactive melt has been confirmed by eitherusing an optical microscope with transmitted light or subjecting it tothe x-ray diffraction (XRD) technique to verify the composition of thisproduct (FIG. 1). FIG. 1 shows no peaks that would indicate the presenceof crystal structures. It is completely different from the XRD patternof either the original contaminated sediments (FIG. 2) with major peaksof quartz, chlorite, illite and mica (as indicated on the figure), orcommercial portland cement with major peaks of C₂ S, C₃ S and alite asshown in FIG. 3, or blended cements (40:60 and 70:30 weight percentblends of reactive melt and portland cement) with somewhat smaller peaksdue to dilution of the portland cement component by the amorphousreactive melt (FIGS. 4 and 5, respectively).

One product (reactive melt) thus formed when a sediment or soil (majormineral elemental oxide component of samples of sediment from NewtownCreek of New York and a Superfund site soil from Illinois are shown inTable 1) has been remediated is reactive in nature and its chemicalcomposition may be generally stated as:

    ______________________________________    Calcium Oxide (CaO)  20 to 40 wt %    Silica (SiO.sub.2)   45 to 65 wt %    Alumina (Al.sub.2 O.sub.3)                          5 to 20 wt %    Ferric Oxide (Fe.sub.2 O.sub.3)                          2 to 10 wt %    Fluxing Agent         0 to 5 wt %    ______________________________________

                  TABLE 1    ______________________________________    MAJOR MINERAL COMPOSITION OF SEDIMENT    Component           Sediment Soil    ______________________________________                        wt %    SiO.sub.2           51.33    65.07    Al.sub.2 O.sub.3    10.58    5.35    Fe.sub.2 O.sub.3    6.26     2.96    CaO                 2.03     7.38    MgO                 2.11     4.18    SO.sub.3            0.41     0.29    Na.sub.2 O          2.77     0.54    K.sub.2 O           1.97     1.52    TiO.sub.2           0.72     0.28    P.sub.2 O.sub.5     0.54     0.09    Mn.sub.2 O.sub.3    0.06     0.07    SrO                 0.03     0.03    Loss On Ignition (950° C.)                        20.43    12.24    Other (By Difference)                        0.76     0.00    TOTAL               100.00   100.00    ______________________________________

Other minor chemical composition of the reactive melt includes magnesia(MgO), alkalies (Na₂ O and K₂ O), sulfur trioxide (SO₃) present asgypsum, halogens present as halogenated inorganics, phosphorus oxide (P₂O₅), titanium oxide (TiO₂), strontium oxide (SrO) etc. and heavy metals.The melting point of the reactive melt bounded by the above chemicalcomposition is between the temperatures of about 1150° C. to about 1400°C.

The comminuted reactive melt evinces cementitious properties either byreaction with aqueous alkaline solution (Example I) or by blending itwith materials such as portland cement (Examples II and III). The weightratio of reactive melt to portland cement for the production ofconstruction grade blended cements ranges from 10 parts of reactive meltto 90 parts of portland cement up to 70 parts of reactive melt to 30parts of portland cement.

In the molten phase, silica (SiO₂) by itself and in chemical combinationwith other oxides such as alumina (Al₂ O₃), ferric oxide (Fe₂ O₃),sodium oxide (Na₂ O), lime (CaO) etc. forms a silicate network thatincorporates heavy metal atoms. The amount of a specified heavy metalthat can be incorporated in the silicate network depends on thesimilarity of that heavy metal to other atoms already present in thenetwork. The elemental substitution can be estimated by the comparisonof "indices of ionic replacement" calculated from the electrovalency,ionic radius, coordination number and electronic configuration of thecations (Jack Green, "Geochemical Table of the Elements," Bulletin ofthe Geological Society of America, Vol. 70, pp. 1127-1184, September1959). The indices of ionic replacement of all cations of concern arepresent in Table 2.

                  TABLE 2    ______________________________________    INDICES OF IONIC REPLACEMENT    ______________________________________    K.sup.+           0.03       Fe.sup.+2                             0.14     Fe.sup.+3                                           0.22    Ag.sup.+           0.04       Cu.sup.+2                             0.14     W.sup.+4                                           0.28    Na.sup.+           0.06       Sn.sup.+2                             0.14     Mo.sup.+4                                           0.28    Ba.sup.+2           0.07       Ni.sup.+2                             0.14     Ti.sup.+4                                           0.28    Pb.sup.+2           0.08       Mg.sup.+2                             0.14     Se.sup.+4                                           0.31    Sr.sup.+2           0.08       U.sup.+4                             d.19     Al.sup.+3                                           0.35    Ca.sup.+2           0.09       Zr.sup.+4                             0.20     Si.sup.+4                                           0.48    Cd.sup.+2           0.09       Mn.sup.+3                             0.21     Se.sup.+6                                           0.49    Hg.sup.+2           0.12       Cr.sup.+3                             0.22     As.sup.+5                                           0.60    Mn.sup.+2           0.13                       P.sup.+5                                           0.62    Zn.sup.+2           0.14    ______________________________________

Referring to Table 2, Ag⁺, Ba⁺², Pb⁺², Sr⁺² and Cd⁺² tend to substitutefor alkali metals; Hg⁺², Mn⁺², Zn⁺², Cu⁺² Sn⁺² and Ni⁺² tend tosubstitute for Mg⁺² and Fe⁺² ; Cr⁺³ tends to substitute for Fe⁺³ ; andso on.

Rapidly cooling a melt causes distortion of the silicate network; athigh cooling rates, the silicate network structure in the solidifiedmelt becomes highly irregular and its molecules are frozen intodisordered noncrystalline glass. When the network irregularity is high,the chances for the heavy metal cations having different indices ofionic replacement from other cations already present in the network tobecome incorporated are enhanced.

The stability of the solidified melt depends on the strength of itssilicate network structure within which the heavy metal impurities areincorporated. This strength can be estimated by the calculating molaracidity of the melt, which is the molar ratio of the sum of the melt'sacidic oxides to the sum of its basic oxides. Besides silica, othercommon acidic oxides in the melt are Al₂ O₃, TiO₂, Fe₂ O₃, P₂ O₅, Cr₂ O₃and ZrO₂. Common basic oxides in the melt include CaO, MgO, Na₂ O, K₂ O,FeO, sulfide and chloride. If the molar acidity of the melt is high, thesilicate network structure will be strong and the melt will be stable.For example, a typical Type I portland cement containing 21.3 wt % SiO₂,5.3 wt % Al₂ O₃, 2.3 wt % Fe₂ O₃, 65.2 wt % CaO, 2.9 wt % MgO and 3.0 wt% SO₃ has a molar acidity of 0.33. A typical reactive melt has a molaracidity that ranges from about 1.0 to about 2.5, thus it is moreenvironmentally stable than portland cement.

Small-scale leachability tests (per the Toxicity Characteristic LeachingProcedure, or TCLP) Anon. Analyt. Control, "TCLP: Improved Method,"12(1), 1-6, publ. bu NUS Corp., Pittsburgh, Pa., 1987. were utilized toconfirm findings of this invention therefrom. The TCLP test results fromreactive melt, blended cement, portland cement and their mortarspecimens are present in Examples IV to VIII.

In order to demonstrate the metal incorporation aspects of the subjectinvention, chromium oxide (Cr₂ O₃) was admixed with the raw materialsused to produce samples of both reactive melt and portland cement. Theseare discussed in Examples IV and VI. The level of chromium in thereactive melt was determined to be about 1110 mg/kg (Table 5) and thatof the portland cement was determined to be 307 mg/kg (Table 9). Theleachability of each sample was determined per the TCLP test (pHadjusted); the results are presented in Tables 6 and 10. The chromiumleached from the reactive melt at 0.94 mg/L. The chromium leached fromthe portland cement at 11.8 mg/L, which is well above the TCLPregulatory limit for chromium of 5 mg/L. Comparing the original chromiumcontents of each sample with their resulting leachabilities, shows thatthe reactive melt is roughly 45 times less leachable than the portlandcement.

The blended cement product made from reactive melt has thecharacteristic of rapidly consuming hydrated lime Ca(OH)₂ ! present inthe portland cement component of the blended cement, when compared tothe rate of disappearance of hydrated lime present in conventionalportland cement. This significantly improves the durability of concreteor mortar prepared with blended cement from reactive melt by essentiallyeliminating harmful side reactions, such as the alkali-silica reaction(ASR). This is demonstrated and discussed in Example IX.

EXAMPLE I

One part of the ground reactive melt was mixed with 2.75 parts of sandand 0.484 part of 20 weight percent NaOH aqueous solution to produce amortar. The mortar was cast as 5-cm (2-inch) cubes and cured under moistconditions at 55° C. for 23 hours. Thereafter, the samples were demoldedand tested for compressive strength within an hour. A strength of 21.4MPa (3100 psi) is reported as the hydraulic activity of the reactivemelt. This indicated that the reactive melt is reactive and cementitiousin nature. The procedure and mortar recipe are part of an ASTM (AmericanSociety for Testing and Materials) standard C-1073.

EXAMPLE II

Forty (40) weight percent of the finely ground (about 4000 cm² /g)reactive melt was blended with sixty (60) weight percent of Type Iportland cement to meet the Type IP/P blended cement specifications asper the ASTM standard C-595. It should be noted that performanceenhancing additives were not added to the blend. One part of the blendedcement was then mixed with 2.75 parts of sand and 0.484 part ofdeionized water as prescribed in ASTM standard C-109 procedure toproduce mortars. The mortars were cast as 5-cm (2-inch) cubes and leftovernight in a moist room at ambient temperature. Thereafter, the cubeswere demolded and cured in saturated lime-water solution. Thecompressive strengths tested after 3, 7 and 28 days are comparable to,or greater than the ASTM required levels. The results presented in Table3 are the average of three separate, compressive strength tests.

                  TABLE 3    ______________________________________    COMPRESSIVE STRENGTHS OF TYPE IP/P BLENDED CEMENT    PRODUCED FROM 40 WT % REACTIVE MELT AND    60 WT % TYPE I PORTLAND CEMENT           TYPE IPIP           REACTIVE    TEST   MELT:PORTLAND  ASTM RANGE  ASTM FOR    PERIOD CEMENT = 40:60 FOR TYPE IP/P                                      TYPE I**    ______________________________________           MPa (psi)     3-day 13.44 (1950)   12.5 (1810) 12.0 (1740)                          (for Type IP only)     7-day 18.82 (2730)   10.4-19.4*  19.0 (2760)                          (1510-2810)    28-day 31.85 (4620)   20.7-24.2*  28.0 (4060)                          (3000-3510)    ______________________________________     *Lower values are ASTM requirements for Type P; higher values are for Typ     IP blended cements.     **For crosscomparison purposes, the strength requirement for general     purpose Type I portland cement has also been included in Table 3 from AST     standard C150 (Tables 3 and 4).

EXAMPLE III

The mortar cubes were prepared according to the procedure of Example IIwithout adding any performance enhancing additives except that seventy(70) weight percent of the finely ground reactive melt was blended withthirty (30) weight percent of Type I portland cement to produce modifiedType P blended cement. Type P is blended cement for concreteconstruction where high strength at early age is not required. ASTM doesnot specify a 3-day compressive strength requirement for the modifiedType P blended cement.

                  TABLE 4    ______________________________________    COMPRESSIVE STRENGTHS OF MODIFIED TYPE P    BLENDED CEMENT PRODUCED FROM 70% REACTIVE MELT    AND 30% TYPE I PORTLAND CEMENT                MODIFIED TYPE P                REACTIVE    TEST        MELT:PORTLAND   ASTM    PERIOD      CEMENT - 70:30  FOR TYPE P    ______________________________________     3-day       6.21 (900)     Not Specified     7-day      10.41 (1510)    10.4 (1510)    28-day      22.41 (3250)    20.7 (3000)    ______________________________________

EXAMPLE IV

The metal analysis of a raw dredged sediment and reactive melt arepresented in Table 5 and the results of Toxicity Characteristic LeachingProcedure (TCLP) tests on the reactive melt are presented in Table 6.The metal analysis of the reactive melt leachate indicated that most ofthe metals are retained in the reactive melt silicate network due to themelting-reaction stages of the process. Some metals such as arsenic andmercury are volatilized during the thermal treatment and are captureddownstream in the requisite air pollution control devices.

                  TABLE 5    ______________________________________    METAL ANALYSIS OF RAW DREDGED SEDIMENT    AND REACTIVE MELT                  Raw Dredged                             Cr-Dosed    Component     Sediment   Reactive Melt    ______________________________________                  mg/kg    Arsenic       33         <5    Barium        192        --*    Cadmium       37         <5    Chromium      377        1110    Lead          617        130    Mercury       1.3        <5    Selenium      <3.24**    <5    Silver        18         <10    ______________________________________     *Not analyzed     **< indicates below the analytical detection limit for the analyte

                  TABLE 6    ______________________________________    METAL ANALYSIS OF REACTIVE MELT LEACHATE    AND THE TCLP REGULATORY LIMIT             Cr-Dosed    Component             Reactive Melt Leachate                            TCLP Regulatory Limit    ______________________________________             mg/L    Arsenic  <0.1*          5    Barium   <0.5           100    Cadmium  <0.01          1    Chromium 0.94           5    Lead     <0.05          5    Mercury  <0.001         0.2    Selenium <0.1           1    Silver   <0.01          5    ______________________________________     *< indicates below the analytical detection limit for the analyte

EXAMPLE V

The metal analyses were performed according to the procedure of ExampleIV except that a blended cement (reactive melt:portland cement=40 wt%:60 wt %) was used instead of reactive melt. The results are presentedin Table 7. The results of leachability tests are presented in Table 8.

                  TABLE 7    ______________________________________    METAL ANALYSIS OF RAW DREDGED SEDIMENT    AND BLENDED CEMENT                 Raw Dredged    Component    Sediment   Blended Cement    ______________________________________                 mg/kg    Arsenic      33         9.22    Barium       192        --*    Cadmium      37         1.59    Chromium     377        480    Lead         617        35.8    Mercury      1.3        <0.07    Selenium     <3.24**    <0.94    Silver       18         2.66    ______________________________________     *Not analyzed     **< indicates below the analytical detection limit for the analyte

                  TABLE 8    ______________________________________    METAL ANALYSIS OF BLENDED CEMENT LEACHATE AND    THE TCLP REGULATORY LIMIT                 Blended Cement                             TCLP    Component    Leachate    Regulatory Limit    ______________________________________                 mg/L    Arsenic      <0.1*       5    Barium       <0.5        100    Cadmium      <0.01       1    Chromium     0.2         5    Lead         <0.05       5    Mercury      <0.001      0.2    Selenium     <0.1        1    Silver       <0.01       5    ______________________________________     *< indicates below the analytical detection limit for the analyte

EXAMPLE VI

The metal analyses were performed according to the procedure of ExampleIV except that a sample of portland cement was used instead of reactivemelt. The results are presented in Table 9. The results of leachabilitytests are presented in Table 10.

                  TABLE 9    ______________________________________    METAL ANALYSIS OF RAW DREDGED SEDIMENT    AND PORTLAND CEMENT                 Raw Dredged                            Cr-Dosed    Component    Sediment   Portland Cement    ______________________________________                 mg/kg    Arsenic      33         <2    Barium       192        51.6    Cadmium      37         <5    Chromium     377        307    Lead         617        55    Mercury      1.3        <5    Selenium     <3.24*     <5    Silver       18         <10    ______________________________________     *< indicates below the analytical detection limit for the analyte

                  TABLE 10    ______________________________________    METAL ANALYSIS OF PORTLAND CEMENT LEACHATE    AND THE TCLP REGULATORY LIMIT                Cr-Dosed Portland                             TCLP Regulatory    Component   Cement Leachate                             Limit    ______________________________________                mg/L    Arsenic     <0.1*        5    Barium      <0.5         100    Cadmium     <0.01        1    Chromium    11.8         5    Lead        <0.05        5    Mercury     <0.001       0.2    Selenium    <0.1         1    Silver      <0.01        5    ______________________________________     *< indicates below the analytical detection limit for the analyte

EXAMPLE VII

Representative samples of portland cement mortar and blended cementmortar were analyzed by the x-ray diffraction (XRD) technique to verifythe compound composition. The XRD results presented in FIGS. 6 and 7compare the differences in the XRD patterns. Since mortar is comprisedprincipally of silica sand, many of the major peaks exhibited are due toquartz and similar crystals.

EXAMPLE VIII

The metal analyses were performed according to the procedure of ExampleIV except that the reactive melt mortar specimen, the portland cementmortar specimen and the blended cement mortar specimen were used.

                  TABLE 11    ______________________________________    METAL ANALYSIS OF REACTIVE MELT MORTAR SPECIMEN    AND PORTLAND CEMENT MORTAR SPECIMEN    Com-   Cr-Dosed Reactive                        Cr-Dosed Portland                                     Blended Cement    ponent Melt Mortar  Cement Mortar                                     Mortar    ______________________________________           mg/kg    Arsenic           3.5          <2           <5    Barium 109          14.3         56.5    Cadmium           <5           <5           <5    Chromium           435          146          145    Lead   17           16           13    Mercury           <5           <5           <5    Selenium           <5           <5           <5    Silver <10          <10          <10    ______________________________________     *< indicates below the analytical detection limit for the analyte

                  TABLE 12    ______________________________________    METAL ANALYSIS OF REACTIVE MELT MORTAR AND    PORTLAND CEMENT MORTAR LEACHATES VERSUS    THE TCLP REGULATORY LIMIT           Cr-Dosed  Cr-Dosed             TCLP           Reactive  Portland             Regu-    Com-   Melt Mortar                     Cement Mortar                                Blended Cement                                          latory    ponent Leachate  Leachate   Mortar Leachate                                          Limit    ______________________________________           mg/L    Arsenic           <0.1*     <0.1       <0.1      5    Barium <0.5      <0.5       <0.5      100    Cadmium           <0.01     <0.01      <0.01     1    Chromium           1.4       3.6        <0.1      5    Lead   <0.05     <0.05      <0.05     5    Mercury           <0.001    <0.001     <0.001    0.2    Selenium           <0.01     <0.1       <0.1      1    Silver <0.01     <0.01      <0.01     5    ______________________________________     *< indicates below the analytical detection limit for the analyte

EXAMPLE IX

The blended cement product made from reactive melt has thecharacteristic of rapidly consuming hydrated lime Ca(OH)₂ ! present inthe portland cement component of the blended cement, when compared tothe rate of disappearance of hydrated lime present in conventionalportland cement. This significantly improves the durability of concreteor mortar prepared with blended cement from reactive melt by essentiallyeliminating harmful side reactions, such as the alkali-silica reaction(ASR). In this example, paste prepared from either blended cement (fromreactive melt) or samples of portland cement and water were analyzed bydifferential scanning calorimetry (DSC) to determine the disappearanceof Ca(OH)₂ during the initial stages of curing from 3 to 28 days.

Other benefits and advantages of the subject invention will beunderstood by the following detailed description and the accompanyingProcess Flow Drawings, in which:

As stated, a process of the present invention involves introducing rawfeed materials such as contaminated sediments and soils, lime, metaloxides and fluxing agents that contain chemical compounds necessary forthe production of reactive melt into a melter in proper proportions.

The most common source of lime is limestone which contains primarilycalcium carbonate (CaCO₃). When heated to about 900° C., this compounddecomposes into lime (CaO) and carbon dioxide (CO₂), the latter which,being a gas, normally escapes from the process unaffected. Usually, thelimestone is preheated prior to its introduction into the melter, notonly to drive off the carbon dioxide, but to also place lesser energydemands on the melter as well. Other naturally occurring materials suchas aragonite, chalk, marl, cement rock, shale and marine shells areequally suitable for use as a raw feed material in the process.

The raw feed materials also include a source of silica; excellentsources of silica are contaminated sediments and soils. The silicasource can be introduced into the melt as fines, whether at ambienttemperature, but preferably preheated.

The raw feed materials, in addition to including a source of lime and asource of silica, also include a source of alumina, a source of ferricoxide and a source of a fluxing agent such as calcium fluoride, althoughthe amount of such materials that is useful is considerably less thanthe amount of lime or silica.

Other materials may appear in minor quantities in the reactive melt asnoted before and may be also present in the various feed materials.These include compounds of alkalis (sodium and potassium) and of sulfur,titanium, magnesium, manganese, phosphorus, barium and strontium.

Within the melter, the feed materials combine and react chemically sothat the formed melt, when withdrawn and quickly cooled, has appropriateproportions. Toxic metals such as lead and cadmium are incorporated andimmobilized within the amorphous silicate network.

The melting, combining and reacting of the above feed material for thereactive melt manufacture can be carried out with a specially builtcupola furnace (FIG. 8), a natural gas-fired melting furnace (FIG. 9),an electric melting furnace (FIG. 10), or other melting devices.

A cupola 10 is a vertical, cylindrical shaft furnace similar to a blastfurnace and efficient conversion-melting is its principal function.Cupola 10 comprises a cylindrical water-cooled steel shell 12 lined withrefractory materials, equipped with a windbox (winddrum, bustle, notshown) and water-cooled tuyeres 14 to provide for delivery and admissionof air or oxygen mixtures into the shaft. At least part of the air oroxygen mixture supply is continuously bubbled through the melting zonelocated at the bottom of the cupola 10. Charging doors are provided atupper levels and holes or spouts 18 near the bottom allow the moltenmaterial to flow out.

The zone of oxygen disappearance in which the overall reaction

    C+O.sub.2 →CO.sub.2

is predominant, is referred to as the oxidation zone or combustion zone.

    C+O.sub.2 →CO.sub.2 ΔH=-94 kcal/mole

Heat generated by the reaction in this zone accomplishes the meltingprocess. The temperature of the melting zone 16 is maintained at about1150° C. to 1500° C. The temperature of the combustion zone ranges fromthe melting temperature down to about 1000° C. The melting temperaturecan vary dependent principally on the materials comprising the reactivemelt. The combustion zone also provides from about 0.5 to about 4seconds residence time for flue gases to achieve high thermaldestruction of organic contaminants.

Above the combustion zone is a heat transfer zone where the limestonedecomposes to quicklime at about 870° C. to 1000° C. The quicklime alsoacts as a filter to trap particulates and entrained nonvolatile heavymetals from the melter flue gases. The heat transfer zone can comprise aseparate piece of equipment, such as a vertical shaft kiln, if desired.

Above the heat transfer zone is a preheating zone which may be aseparate piece of equipment 28, in its upper region. In the preheatingzone a charge of limestone is heated to about 870° C. The off gasesleave the preheating zone at a temperature of about 250° C. to about350° C. Additional waste heat can be recovered from the off gases toremove excess moisture content in the sediments and soils before theyare fed into the melter. Drying of wet feeds can be carried out in aseparate piece of equipment (not shown in FIGS. 8, 9 and 10) attemperatures of about 55° C. to 95° C. in order to minimize thevolatilization of chlorinated and other hazardous compounds into theflue gas. If necessary, the flue gas can be scrubbed before it is ventedinto the atmosphere.

One of the advantageous features of the above process is that thecounterflow preheating of the charge material becomes an inherent partof the melting process. The upward flowing hot gases come into intimatecontact with the descending burden, allowing direct and efficient heatexchange to take place.

Due to the emissions emerging from a cupola melting furnace, at somelocations where the air emission regulations are more stringent, naturalgas can be used as fuel to replace coke in a natural gas-fired meltingfurnace. Another reason for using natural gas can result from the ashcontamination caused by the coke or coal used in the cupola.

As shown in FIG. 9, a natural gas-fired melting furnace 30 consists of awater-cooled, refractory-lined vertical, cylindrical steel vessel 31 anda nonconsumable hollow steel lance 32. The furnace 30 is also equippedwith feed ports 34 and 35 and gas exit 35 at upper levels and tap hole18 slightly above the bottom of the furnace. The outer surfaces of thefurnace wall and bottom is chilled with a stream of water flowing in thecooled jacket 36.

Additive components (includes alumina, bauxite, ferric oxide and fluxingagent) and quicklime are gravity fed through the feed ports 34 and 35.The lance 32 injects natural gas (or fuel oil) and an excess amount ofoxygen mixture or air into the vessel 30. The mechanism by which meltingis accomplished in the melting furnace is heat release by combustion ofnatural gas and oxygen:

    CH.sub.4 +2O.sub.2 →CO.sub.2 +2H.sub.2 OΔH=-192 kcal/mole

A protective coating of frozen slag 37 makes the lance nonconsumable.For normal operation, the lance tip is submerged into the molten bath 16in order to provide proper mixing and achieve high thermal destructionand removal efficiencies of the organic contaminants.

Alternatively, as shown in FIG. 10, an electric melting furnace 40 canbe used to achieve the same purpose. An electric melting furnace 40continuously melts the feed materials used for reactive meltmanufacturing and including a refractory lined furnace vessel 42. Aplurality of electrodes 44 extending into the furnace vessel from itsside or top is illustrated schematically in FIG. 10. Each one of theelectrodes 44 can be moved into the melt bath 16 or away from it inmillimeter increments by a worm drive mechanism (not shown) so as toadjust to a certain immersion depth. For obtaining a high meltingperformance, the electric melting furnace is designed as a 3-phasealternating current furnace. The introduction of energy can be effectedby resistance heat.

The immersion depths of the electrodes 44 are adjusted for constantperformance, with the electrodes being individually controlled. The heatfrom the electrodes 44 melts the feed materials including the wastematerials at a temperature of about 1150° C. to 1500° C. and moltenreactive melt of substantially uniform composition is formed as a resultof the liquid phase oxide reactions. The molten reactive melt from ahotter region below the surface is continuously withdrawn from thefurnace vessel through tapping device 26. The location of the tappingdevice is preferred to be slightly above the bottom of the furnacevessel.

The temperature range of the combustion zone in an electric meltingfurnace or a natural gas fired melting furnace is similar to that in acupola, starting from the melting temperature to about 1000° C. Theresidence time between about 0.5 to 4 seconds of the flue gas generatedin the heating step is useful to enable high thermal destruction oforganic contaminants in the combustion zone. Similar to the cupola, thelimestone to quicklime reaction can also be conducted in a separatepiece of equipment 28 (e.g., a vertical shaft kiln). The hot gases fromthe combustion zone will provide the energy required for the limestonedecomposition and the hot quicklime is being charged continuously intothe melting furnace.

    CaCO.sub.3 →CO.sub.2 +CaOΔH=42.82 kcal/mole

The quicklime vertical shaft kiln 28 can be fired by fuel oil or naturalgas, if additional energy is required.

The molten reactive melt through the outlets 18 of the cupola; theelectric melting furnace; or the natural gas fired melting furnace isgenerally kept at a temperature exceeding about 1300° C. The melt israpidly quenched in moist air, steam or water to prevent crystallizationand enhance heavy metal incorporation. The quenched melt is thenpulverized to yield the product, a reactive melt, which can then bemixed with portland cement or other cements for the production ofblended cements. The quenched melt may be pulverized to a particle sizein the longest dimension of 1-100 microns, and preferably a particlesize of 5-40 microns to obtain a quicker setting of the resultingblended cement.

A contemplated process utilizes a feed material, without preprocessingrequirements such as dewatering and sizing, of all types of contaminatedestuarine, river, ocean, or lake sediments and contaminated soils (sand,clay, or shale). Contaminated sediments and soils are fed either to themelting zone or the combustion zone of the furnaces depending on thenature and type of the contaminants; where the organiccontaminants-depleted sediments and soils plus proper amounts of lime,metal oxides and fluxing agent are incorporated into the melt and thusform the subsequent reactive melt.

Because of the presence of calcium in the melt, no HCl, chlorine orSO_(x) could be formed. Chlorine (if any) or chlorine compounds, SO_(x)(if any) and NO_(x) in the off gas are typically scrubbed or washed.Highly volatile heavy metals such as mercury and arsenic may be removedfrom the off gas by a simple in-line bag-type filter or activated carbonor silver or sulfur impregnated activated carbon. Volatilized compoundsof sodium, potassium and phosphorus in the off gas are scrubbed andremoved. Entrained nonvolatile heavy metals in the off gas are alsoscrubbed and returned to the melting zone for incorporation pursuant tothe subject invention.

All of the melting furnaces suggested are very suitable for usingshredded scrap tire as waste feed material and energy sources as thesefurnaces operate at very high temperatures and have long residencetimes. The furnace temperatures typically exceed about 1300° C. (2372°F.). High temperatures, long residence times and an adequate supply ofoxygen ensure complete burnout of organics, which precludes thesubsequent formation of dioxins and furans, a primary consideration insolid waste combustion.

In addition, the reactive melt production process of the subjectinvention can utilize the iron contained in the steel beads and belts oftires. The steel does not change the quality of the reactive meltproduct, because large quantities of iron compound are already presentas one of the main ingredients. In some cases, when insufficient ironcompound is present in the feed materials, the iron contained insteel-belted tires can help to improve the properties of the finalreactive melt product. The sulfur contained in the tires reacts with thelimestone to form gypsum which is also one of the ingredients needed forreactive melt production. This reaction also alleviates concerns aboutthe SO_(x) air emission problem from sulfur in the rubber tires.

In general, burning scrap tires in the furnace can improve furnaceperformance, reduce natural gas requirements and achieve more stableoperations due to the higher energy content and more uniform compositionof tires. When ash contamination is not a problem and the air emissionlevels are properly monitored, shredded scrap tires can be added to thefeed materials to reduce fuel and electric power consumption. This canbe important when the feed is wet as in the case of estuarine sediments.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes can be made and equivalents can be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications can be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiments disclosed as the best modescontemplated for carrying out this invention, but that the inventionincludes all embodiments and equivalents falling within the scope of theappended claims.

Various features of the invention are set forth in the following claims.

What is claimed:
 1. An environmentally stable substantially non-leachingcement product of a process for thermo-chemical remediation anddecontamination of sediments and soils contaminated with organicmaterials as well as inorganic contaminants and heavy metals, theprocess comprising the steps of:a) blending said contaminated sedimentsor soils with a calcium oxide source, alumina, ferric oxides and fluxingagent to form a mixture; b) heating the mixture above the meltingtemperature of said mixture to produce a completely molten homogeneousreaction product; c) bubbling oxygen through the molten reaction productfor destruction of said organic contaminants; d) quenching the reactionproduct in the presence of moist air, steam or water to form a reactiveamorphous material having a silicate network, and thereby incorporatinginorganic contaminants and heavy metals within the silicate network; e)pulverizing the reactive amorphous material to form a reactivecementitious powder having a molar acidity of about 1.0 to about 2.5; f)blending the cementitious powder with cement to yield a stable blendedcement which leaches less than 0.01 mg/L, of Cd, and less than 0.05 mg/Lof Pb.
 2. The product of claim 1, wherein said fluxing agent is calciumfluoride.
 3. A generally homogeneous non-leaching reactive cementitiousmelt product which is amorphous and comprising: calcium oxide (CaO),about 20 to 40 wt %; silica (SiO₂), about 45 to 65 wt %; alumina (Al₂O₃), about 5 to 20 wt %; ferric oxide (Fe₂ O₃), about 2 to 10 wt %; andfluxing agent, said melt product leaching less that 0.01 mg/L of Cd, andless than 0.05 mg/L of Pb.
 4. The reactive melt product of claim 3,further including minor chemical components of magnesia (MgO), alkalis(Na₂ O and K₂ O), sulfur trioxide (SO₃) present as gypsum, halogenspresent as halogenated inorganics, phosphorus oxide (P₂ O₅), titaniumoxide (TiO₂) and strontium oxide (SrO).
 5. The reactive melt product ofclaim 3, wherein the melting point of the reactive melt is between thetemperatures of about 1150° to about 1400° C.
 6. The reactive meltproduct of claim 3 further mixed with 2.75 parts of sand and 0.484 partof 20 wt % NaOH aqueous solution for every one part of the reactive meltproduct, to yield a mortar with high compressive strength greater than21.4 Mpa.
 7. The reactive melt product of claim 3 further blended withportland cement to yield a blended cement.
 8. The reactive melt productof claim 3, wherein heavy metals are incorporated in a silicate networkwithin the reactive melt product.
 9. A blended cement comprising amixture of portland cement and a reactive melt product, said reactivemelt product is a generally homogeneous amorphous non-leachingcementitious melt product comprising CaO, SiO₂, Al₂ O₃, Fe₂ O₃ and CaF₂,the weight ratio of reactive melt product to portland cement being fromabout 10 parts of reactive melt product to about 90 parts of portlandcement up to about 70 parts of reactive melt product to about 30 partsof portland cement, said melt product leaching less than 0.01 mg/L ofCd, and less than 0.05 mg/L of Pb.
 10. The blended cement of claim 9,wherein the reactive melt product component consumes hydrated limepresent in said portland cement.
 11. The blended cement of claim 9,wherein said reactive melt product has the composition of: calcium oxide(CaO), about 20 to 40 wt %; silica (SiO₂), about 45 to 65 wt %; alumina(Al₂ O₃), about 5 to 20 wt %; ferric oxide (Fe₂ O₃), about 2 to 10 wt %;and fluxing agent, about 0 to 5 wt %.